The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for controlling the system of the vehicle by determining attitude of the vehicle using suspension height sensors.
In modern vehicle control systems for automotive vehicles, the vehicle attitude control systems directly influence the comfort, handling and safety of the vehicle. For example, the ride comfort of a vehicle requires regulating the dynamic variation of the vehicle body pitch and roll attitudes; the rollover prevention (active safety) requires regulating the roll attitude between the vehicle car body and the average road surface; the air bag requires determining both the vehicle global roll attitude and its velocity before it is deployed; an active anti-roll-bar may be activated based on the vehicle roll attitude; vehicle pitch attitude may be used to predict vehicle load transfer between front axle and rear axle. The control system uses the available actuators to alter actual vehicle attitude based on the sensed or predicted vehicle body attitudes.
Two types of vehicle attitudes must be distinguished. One is the global attitude, which is relative to an earth frame (also called the inertial frame), sea level, or a flat and horizontal road. The global attitude can be directly related to measurements taken by inertial acceleration sensors or GPS-based angular rate sensors. The other is the relative attitude, which defines the angular positions of the vehicle with respect to the road surface on which the vehicle is driven. Since the relative attitude of the vehicle must be measured with respect to the road surface on which the vehicle rests at any given moment, the angle and slope of which is continuously changing, relative attitude can not be directly related to the output of inertial or GPS-type acceleration sensors.
In order to successfully achieve the desired vehicle attitude control goal as mentioned before, predicting the aforementioned relative and global attitudes with high accuracy from available sensor signals is of great importance.
A vehicle attitude sensing method has been proposed in U.S. Pat. No. 5,408,411. In that patent, a sensor module using six linear acceleration sensors is mounted on the vehicle to get vehicular attitude information. Although this method is able to sense vehicle attitude, the sensor set is believed to provide little advantage in terms of performance and cost.
It would therefore be desirable to provide an attitude control system to predict attitude angle for vehicle dynamics control that includes the interdependency among the roll, pitch, and yaw motions while compensating for long term maneuvers.
The present invention is particularly suited for an automotive vehicle equipped with a yaw stability control system and a controllable suspension system. The sensor set used in a yaw stability control system typically includes vehicle lateral and longitudinal acceleration sensors, and a yaw rate sensor. The controllable suspension system used here is equipped with four suspension height sensors mounted at the four corners of the vehicle. The yaw stability control system aims to prevent a vehicle from spinning-out during driving, and to regulate the vehicle side-slip angle (which could be thought of as a relative yaw attitude with respect to the desired course of the vehicle). The controlled suspension systems aims to improve vehicle ride comfort and provide a leveling function. The suspension height sensors are used to provide feedback signals so that vehicle leveling and suspension controlling may be performed. The present invention employs the suspension height sensors to obtain the pitch and roll characteristics of the vehicle. That is, the present invention senses vehicular relative attitude with respect to the average road surface of various terrains, and vehicular absolute attitude with respect to the sea level for vehicular attitude control applications. Advantageously, the system can be used for roll stability control, controllable suspensions, active anti-roll-bars, and other vehicle dynamics control systems.
In one aspect of the invention, a control system for an automotive vehicle includes a lateral acceleration sensor, a yaw rate sensor, four suspension height sensors generating four suspension height signals, and a longitudinal acceleration sensor. The controller determines a roll characteristic from the suspension height signals, the lateral acceleration signal and a pitch characteristic from the four suspension height signals and the longitudinal acceleration signal.
In a further aspect of the invention, a method of controlling a safety device for an automotive vehicle having a body comprises measuring a lateral acceleration of the vehicle body; measuring a longitudinal acceleration of the vehicle body; measuring a yaw rate of the vehicle body; measuring four suspension height signals corresponding to the four suspension heights of the four corners of the vehicle; determining a roll angular rate of the vehicle body from the suspension height signals and the lateral acceleration signal; determining a pitch angular rate of the vehicle body from the suspension height signals and the longitudinal acceleration signal; determining the global roll and pitch attitude angles based on the predicted roll and pitch angular rate signals; determining the relative roll and the pitch attitude angle of the vehicle body with respect to the average road surface based on the four suspension height signals; and activating a safety device in response to the estimated relative roll angle, the estimated relative pitch angle, the estimated global roll and estimated global pitch angle.
The present invention aims to estimate and predict the vehicular attitude used in vehicle attitude control systems such as a controllable suspension system, a roll stability control system, a yaw stability control system, an active anti-roll-bar system and other vehicle dynamics control systems. The estimated and predicted variables are used for setting the feedback control action flag and as the feedback signals to construct the desired control command to activate the actuators.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.